The invention relates to a vehicle with an N-phase electric motor, with a first onboard electrical subsystem and with a second onboard electrical subsystem, the electric motor comprising a rotor and a stator system, the first onboard electrical subsystem comprising an inverter, the stator system being associated with the inverter, and the electric motor being operable with an inverter controller according to the principle of field-oriented control.
In a vehicle, components that constitute electrical power consumers are usually supplied with power by an onboard electrical system with a nominal voltage level of 14 volts. A secondary 12-volt energy storage, which assumes the function of a power source or the function of an energy sink in the onboard electrical system depending on the operational situation, and a 14-volt generator are then designed to generate electrical power output of 2-3 kW needed in the vehicle.
Especially if several consumers with an elevated a higher power consumption output requirement are integrated into the onboard electrical system of the vehicle, the onboard electrical system can have two onboard electrical subsystems. Then a DC/DC converter transfers electrical power between the two onboard electrical subsystems. The electric motor, which can also be motor-operable in a vehicle with electrified power train, has, as at least one energy store per onboard electrical subsystem, the function of an electrical power source or sink in the vehicle. Such an onboard electrical system topology is disclosed in DE 102 44 229 A1, for example.
It is an object of the invention to describe an improved vehicle with a multiphase electric motor, with a first onboard electrical subsystem and with a second onboard electrical subsystem, the electric motor comprising a rotor and a stator system, the first onboard electrical subsystem comprising an inverter, the stator system being associated with the inverter, and the electric motor being operable with an inverter controller according to the principle of field-oriented control.
This object is achieved by a vehicle according to the independent claims. Advantageous embodiments and developments of the invention follow from the dependent claims.
According to the invention, the stator system is embodied in a star circuit, the star point is connected to the second onboard electrical subsystem or can be connected via a star point switch to the second onboard electrical subsystem, and the inverter controller comprises a current controller and a star point controller.
This means that the star point of the electric motor can be connected via the star point switch with the electrical potential of the second onboard electrical subsystem or permanently connected. This enables current to flow over the star point, which is referred to as star point current. The star point current is thus introduced into the motor as an additional degree of freedom, provided that it is connected via the star point switch to the second onboard electrical subsystem. The control principle of the electric motor is expanded by adding a star point controller to the inverter controller, which controls the electric motor and has a current controller for the stator system. By virtue of the star point controller, the current can be controlled via the star point. For example, the second onboard electrical subsystem can be formed by electrical consumers or, alternatively or in addition, by another stator system in the star or delta circuit of an electric motor. In addition, a DC link capacitor can be associated with the inverter.
According to one preferred embodiment of the invention, at least one number of N−1 phase currents can be measured from the number of N-phase currents of the stator system, the measured phase currents can be transformed via an enhanced Clarke-Park transformation into a field-oriented current representation with a field-building component, with a torque building component and with a current zero component, the star point current being three times the current zero component.
A permanent electrical connection is to be understood as a non-open and non-openable current path. This means, for example, that diodes can be introduced in the current path.
Accordingly, the electric motor can be controlled according to the principle of field-oriented control, with which a person skilled in the art is familiar. According to this principle, two phase currents of the stator system are measured and transformed via a two-dimensional Clarke-Park transformation into two rotor-fixed current values—like in a three-phase electric motor, for instance. The two rotor-fixed current values refer to a field-building current component and a torque-building current component. The transformation is done by a control unit, e.g., by a control device.
According to one preferred embodiment, two phase currents and the star point current are measured or, alternatively, the three phase currents are measured.
During measurement of the three phase currents, they are fed to an enhanced three-dimensional Clarke-Park transformation, which is a modified version of the two-dimensional Clarke-Park transformation known to a person skilled in the art. Besides the field-building current component and the torque-building current component, a zero current component is obtained as an additional component. This zero current component is one-third of the star point current, i.e., of the current flow over the star point of the electric motor.
In general, that is, in any multiphase electric motor, a number of current measurement points are provided overall by means of current measurement means which corresponds at least to the number N of the phases of the electric motor.
Furthermore, it is especially advantageous if the inverter controller has the field-building current component as a control variable, the torque-building current component as a control variable, the zero current component as a control variable, a first reference current value for the field-building current component as a reference value, and a second reference current value for the torque-building current component as a reference value, and a star point reference current for the star point controller as a reference value, and outputs a first stator control voltage associated with the field-building current component as an actuating variable, outputs a second stator control voltage associated with the torque-building current component as an actuating variable, and outputs a third stator control voltage associated with the zero current component as an actuating variable.
The third reference current value is directly associated with the star point current due to the correlation between the zero current component and the star point current. The third stator control voltage is therefore to be regarded as the actuating variable of the star point controller, while the first and second stator control voltage serve as actuating variables of the stator (current) controller.
According to one especially preferred embodiment of the invention, the current controller and the star point controller are embodied substantially as PI controllers.
The design of the current controller and star point controller as a robust PI controller is especially advantageous due to the controlled system that describes the correlation between the values of the electric motor such as speed, taken torque, incoming torque, angular position of the rotor relative to the stator, magnetic fluxes through stator and rotor as well as phase voltages and phase currents.
Alternatively, control circuits with dynamics and precision comparable to PI controllers and also less complexity can also be used, such as PID controllers or controllers with a feed forward control.
According to another embodiment of the present invention, the N-phase electric motor is embodied as a 3-phase electric motor and the inverter comprises six inverter switches which are arranged in three half bridges for the three phases of the stator system, and the inverter, in a switching cycle according to the principle of pulse-width modulation, switches the phase voltage for each of the phases, the first stator control voltage, the second stator control voltage and the third stator control voltage being transformable by means of an enhanced inverse Clarke-Park transformation into the phase voltages of the stator system to be switched.
The phase voltages to be switched are thus determined by a modified inverse Clarke-Park transformation, the modification of the inverse Clarke-Park transformation corresponding to the modification of the Clarke-Park transformation to the enhanced Clarke-Park transformation. The obtained phase voltages can be switched by the inverter in a pulse-width-modulated manner, i.e., the phase voltage is set through switching of the respective half bridge center to the higher potential of the first onboard electrical subsystem for a certain switching time through opening of the inverter switch between the half bridge center and the lower potential of the first onboard electrical subsystem and closing of the half bridge, the ratio of the switching time to the cycle time being directly proportional to the phase voltage to be set. The phase voltage is thus set in the time average of a cycle.
According to another variant of the invention, the electric motor, with closed star point switch and with a star point current with a direction of flow from the star point to the second onboard electrical subsystem, brings about a transfer of electrical power from the first onboard electrical subsystem to the second onboard electrical subsystem.
This means that, if a target star point current is prescribed for and set in the electric motor that corresponds to a current flow from the star point to the second onboard electrical subsystem, the electric motor acts as a step-down converter.
According to another variant of the invention, the electric motor, with closed star point switch and with a star point current with a direction of flow from the second onboard electrical subsystem to the star point, brings about a transfer of electrical power from the second onboard electrical subsystem to the first onboard electrical subsystem.
This means that, if a target star point current is prescribed for and set in the electric motor that corresponds to a current flow from the second onboard electrical subsystem to the star point, the electric motor acts as a step-up converter.
Furthermore, if the star point switch is closed by prescribing the target star point current and adjusting the star point control voltage, a star point current can be set that corresponds to a current flow from the second onboard electrical subsystem to the star point or from the star point to the second onboard electrical subsystem.
The electric motor thus acts as a bidirectional power controller. This applies both to a rotating and stationary rotor.
A preferred exemplary embodiment of the invention is described below on the basis of the enclosed schematic drawing. Additional details, preferred embodiments and developments of the invention are revealed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.